Helicobacter pylori is the causative agent of peptic ulcer disease and a variety of other diseases in humans, including gastric cancer and mucosal-associated lymphoma. Motility is required for H. pylori to cross the gastric mucous layer and colonize the gastric epithelium, and H. pylori use a cluster of polar flagella to accomplish this. Regulation of flagellar gene expression in bacteria is complex and involves a transcriptional hierarchy that couples the expression of flagellar genes with assembly of the flagellum. The long-term objective of proposed research is to identify mechanisms used by H. pylori to regulate flagellar gene expression. The alternative sigma factor RpoN is needed for transcription of several H. pylori flagellar genes. Transcription of these RpoN-dependent genes also requires the FlgS/FlgR two-component system. Expression of H. pylori RpoN-dependent flagellar genes is linked to the flagellar protein export apparatus as mutations in genes encoding components of the export apparatus interfere with expression the RpoN regulon. The mechanism by which the export apparatus influences expression of the RpoN regulon is unknown. The goal of this project is to identify the molecular mechanism by which the export apparatus controls expression of the H. pylori RpoN flagellar regulon. The working hypothesis is that the export apparatus affects transcription of the H. pylori RpoN regulon by secreting an inhibitor of the RpoN regulon or influencing the activity of the sensor kinase FlgS through protein-protein interactions. This hypothesis will be tested objectively in three specific aims. The first specific aim will determine if a constitutively active form of FlgR bypasses export apparatus mutations to allow expression of RpoN-dependent reporter genes. In the second specific aim H. pylori strains with mutations that lock the export apparatus in a conformation that favors rod-/hook-type substrates will be examined to see how they influence expression of RpoN-dependent reporter genes. The third specific aim will determine if the novel protein HP1042 is an inhibitor of the RpoN regulon by disrupting the gene encoding this protein and determining how this mutation affects expression of RpoN-dependent reporter genes in H. pylori. The proposed work is relevant to NIH's mission of promoting public health in the United States as the results of the studies may lead to identification of new targets for the control or detection of H. pylori. This information is essential to begin to reduce the morbidity and mortality associated with H. pylori infections. PUBLIC HEALTH RELEVANCE: Helicobacter pylori is a causative agent of peptic ulcer disease and other gastric diseases, causing an estimated 1 million hospitalizations and 6,500 deaths each year in the United States. Results of the proposed studies may lead to the identification of new targets for the control or detection of H. pylori, which is important to begin to reduce the morbidity and mortality associated with this significant pathogen.